diff options
Diffstat (limited to 'lld/ELF/SyntheticSections.h')
| -rw-r--r-- | lld/ELF/SyntheticSections.h | 161 |
1 files changed, 126 insertions, 35 deletions
diff --git a/lld/ELF/SyntheticSections.h b/lld/ELF/SyntheticSections.h index fc5ffa3f274..9776f2a32d0 100644 --- a/lld/ELF/SyntheticSections.h +++ b/lld/ELF/SyntheticSections.h @@ -178,12 +178,21 @@ public: bool updateAllocSize() override; void finalizeContents() override; bool empty() const override; - void addEntry(Symbol &Sym, int64_t Addend, RelExpr Expr); - bool addDynTlsEntry(Symbol &Sym); - bool addTlsIndex(); - uint64_t getPageEntryOffset(const Symbol &B, int64_t Addend) const; - uint64_t getSymEntryOffset(const Symbol &B, int64_t Addend) const; - uint64_t getGlobalDynOffset(const Symbol &B) const; + + // Join separate GOTs built for each input file to generate + // primary and optional multiple secondary GOTs. + template <class ELFT> void build(); + + void addEntry(InputFile &File, Symbol &Sym, int64_t Addend, RelExpr Expr); + void addDynTlsEntry(InputFile &File, Symbol &Sym); + void addTlsIndex(InputFile &File); + + uint64_t getPageEntryOffset(const InputFile &F, const Symbol &S, + int64_t Addend) const; + uint64_t getSymEntryOffset(const InputFile &F, const Symbol &S, + int64_t Addend) const; + uint64_t getGlobalDynOffset(const InputFile &F, const Symbol &S) const; + uint64_t getTlsIndexOffset(const InputFile &F) const; // Returns the symbol which corresponds to the first entry of the global part // of GOT on MIPS platform. It is required to fill up MIPS-specific dynamic @@ -195,13 +204,8 @@ public: // the number of reserved entries. unsigned getLocalEntriesNum() const; - // Returns offset of TLS part of the MIPS GOT table. This part goes - // after 'local' and 'global' entries. - uint64_t getTlsOffset() const; - - uint32_t getTlsIndexOff() const { return TlsIndexOff; } - - uint64_t getGp() const; + // Return _gp value for primary GOT (nullptr) or particular input file. + uint64_t getGp(const InputFile *F = nullptr) const; private: // MIPS GOT consists of three parts: local, global and tls. Each part @@ -240,32 +244,110 @@ private: // addressing, but MIPS ABI requires that these entries be present in GOT. // TLS entries: // Entries created by TLS relocations. + // + // If the sum of local, global and tls entries is less than 64K only single + // got is enough. Otherwise, multi-got is created. Series of primary and + // multiple secondary GOTs have the following layout: + // - Primary GOT + // Header + // Local entries + // Global entries + // Relocation only entries + // TLS entries + // + // - Secondary GOT + // Local entries + // Global entries + // TLS entries + // ... + // + // All GOT entries required by relocations from a single input file entirely + // belong to either primary or one of secondary GOTs. To reference GOT entries + // each GOT has its own _gp value points to the "middle" of the GOT. + // In the code this value loaded to the register which is used for GOT access. + // + // MIPS 32 function's prologue: + // lui v0,0x0 + // 0: R_MIPS_HI16 _gp_disp + // addiu v0,v0,0 + // 4: R_MIPS_LO16 _gp_disp + // + // MIPS 64: + // lui at,0x0 + // 14: R_MIPS_GPREL16 main + // + // Dynamic linker does not know anything about secondary GOTs and cannot + // use a regular MIPS mechanism for GOT entries initialization. So we have + // to use an approach accepted by other architectures and create dynamic + // relocations R_MIPS_REL32 to initialize global entries (and local in case + // of PIC code) in secondary GOTs. But ironically MIPS dynamic linker + // requires GOT entries and correspondingly ordered dynamic symbol table + // entries to deal with dynamic relocations. To handle this problem + // relocation-only section in the primary GOT contains entries for all + // symbols referenced in global parts of secondary GOTs. Although the sum + // of local and normal global entries of the primary got should be less + // than 64K, the size of the primary got (including relocation-only entries + // can be greater than 64K, because parts of the primary got that overflow + // the 64K limit are used only by the dynamic linker at dynamic link-time + // and not by 16-bit gp-relative addressing at run-time. + // + // For complete multi-GOT description see the following link + // https://dmz-portal.mips.com/wiki/MIPS_Multi_GOT // Number of "Header" entries. static const unsigned HeaderEntriesNum = 2; - // Number of allocated "Page" entries. - uint32_t PageEntriesNum = 0; - // Map output sections referenced by MIPS GOT relocations - // to the first index of "Page" entries allocated for this section. - llvm::SmallMapVector<const OutputSection *, size_t, 16> PageIndexMap; - - typedef std::pair<const Symbol *, uint64_t> GotEntry; - typedef std::vector<GotEntry> GotEntries; - // Map from Symbol-Addend pair to the GOT index. - llvm::DenseMap<GotEntry, size_t> EntryIndexMap; - // Local entries (16-bit access). - GotEntries LocalEntries; - // Local entries (32-bit access). - GotEntries LocalEntries32; - - // Normal and reloc-only global entries. - GotEntries GlobalEntries; - - // TLS entries. - std::vector<const Symbol *> TlsEntries; - uint32_t TlsIndexOff = -1; uint64_t Size = 0; + + size_t LocalEntriesNum = 0; + + // Symbol and addend. + typedef std::pair<Symbol *, int64_t> GotEntry; + + struct FileGot { + InputFile *File = nullptr; + size_t StartIndex = 0; + + struct PageBlock { + size_t FirstIndex = 0; + size_t Count = 0; + }; + + // Map output sections referenced by MIPS GOT relocations + // to the description (index/count) "page" entries allocated + // for this section. + llvm::SmallMapVector<const OutputSection *, PageBlock, 16> PagesMap; + // Maps from Symbol+Addend pair or just Symbol to the GOT entry index. + llvm::MapVector<GotEntry, size_t> Local16; + llvm::MapVector<GotEntry, size_t> Local32; + llvm::MapVector<Symbol *, size_t> Global; + llvm::MapVector<Symbol *, size_t> Relocs; + llvm::MapVector<Symbol *, size_t> Tls; + // Set of symbols referenced by dynamic TLS relocations. + llvm::MapVector<Symbol *, size_t> DynTlsSymbols; + + // Total number of all entries. + size_t getEntriesNum() const; + // Number of "page" entries. + size_t getPageEntriesNum() const; + // Number of entries require 16-bit index to access. + size_t getIndexedEntriesNum() const; + + bool isOverflow() const; + }; + + // Container of GOT created for each input file. + // After building a final series of GOTs this container + // holds primary and secondary GOT's. + std::vector<FileGot> Gots; + + // Return (and create if necessary) `FileGot`. + FileGot &getGot(InputFile &F); + + // Try to merge two GOTs. In case of success the `Dst` contains + // result of merging and the function returns true. In case of + // ovwerflow the `Dst` is unchanged and the function returns false. + bool tryMergeGots(FileGot & Dst, FileGot & Src, bool IsPrimary); }; class GotPltSection final : public SyntheticSection { @@ -318,7 +400,15 @@ public: DynamicReloc(RelType Type, const InputSectionBase *InputSec, uint64_t OffsetInSec, bool UseSymVA, Symbol *Sym, int64_t Addend) : Type(Type), Sym(Sym), InputSec(InputSec), OffsetInSec(OffsetInSec), - UseSymVA(UseSymVA), Addend(Addend) {} + UseSymVA(UseSymVA), Addend(Addend), OutputSec(nullptr) {} + // This constructor records dynamic relocation settings used by MIPS + // multi-GOT implementation. It's to relocate addresses of 64kb pages + // lie inside the output section. + DynamicReloc(RelType Type, const InputSectionBase *InputSec, + uint64_t OffsetInSec, const OutputSection *OutputSec, + int64_t Addend) + : Type(Type), Sym(nullptr), InputSec(InputSec), OffsetInSec(OffsetInSec), + UseSymVA(false), Addend(Addend), OutputSec(OutputSec) {} uint64_t getOffset() const; uint32_t getSymIndex() const; @@ -341,6 +431,7 @@ private: // plus the original addend as the final relocation addend. bool UseSymVA; int64_t Addend; + const OutputSection *OutputSec; }; template <class ELFT> class DynamicSection final : public SyntheticSection { |
